The invention relates to a voltage-controlled capacitor.
Known voltage-controlled capacitors (varactors) are utilized particularly in voltage-controlled oscillators.
Controlled capacitors of the species are described in the references titled xe2x80x9cA 1.8 GHz CMOS Low-Phase-Noise Voltage-controlled Oscillator with Prescalerxe2x80x9d (Jan Craninckx and M. S. J. Steyaert, IEEE Journal of Solid-State Circuits, vol. 30, No. 12, December 1995) and in xe2x80x9cA Comparison Between Two 1.8 GHz CMOS VCOs Tuned by Different Varactorsxe2x80x9d (Proc. of the European Solid-State Circuits Conference (ESSCIRC""98), pp. 380-83, The Hague, September 1998).
A unique feature of voltage-controlled oscillators is that their frequency can be controlled by a voltage thereat. When they are utilized in the high-frequency band, it is possible to tune their oscillation behavior by a voltage-controlled capacitor, i.e. a varactor.
It is accordingly an object of the invention to provide a voltage-controlled capacitor, that overcomes the above-mentioned disadvantages of the prior art devices of this general type, which defines a lay out for the voltage-controlled capacitor that has an optimally low sensitivity to interference.
With the foregoing and other objects in view there is provided, in accordance with the invention, a voltage-controlled capacitor. The voltage-controlled capacitor has two varactors connected in parallel. The two varactors are connected such that their capacitance is controlled by difference signals.
The object is inventively achieved by equipping a voltage-controlled capacitor such that it contains parallel varactors that are connected such that the capacitance is controlled by difference signals.
It is expedient that the capacitance is controlled by difference signals between the two varactors.
It is advantageous to configure the voltage-controlled capacitor such that one varactor contains an nmos layer sequence, and the other varactor contains a pmos layer sequence.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a voltage-controlled capacitor, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.